JPH03167006A - Pneumatic tire for heavy load - Google Patents

Abstract

PURPOSE:To improve friction force against the ice and snow road surface in particular by forming block patterns on the tread surface, and by specifying tread developing width and the groove area ratio to the tread surface respectively and also by forming a tread section of specific foaming rubber having closed cells therein. CONSTITUTION:A plurality of blocks 3 are formed on the tread surface 10 surrounded by a plurality of main grooves 1 extending in the tire peripheral direction E-E' and a plurality of cross grooves 2 extending in the tire cross direction. In this case, tread developing width TDW is to be set to 80% or more of maximum tire width, and the groove area ratio of the tread surface 10 to 30% through 45%. A tread section is formed of foaming rubber having closed cells therein. The foaming rubber is formed with urea-formaldehyde assistant of quantity less than foaming agent compounded in the foaming rubber compounded, and JIS hardness at a temperature of 10 deg.C is set to 60 through 74, the average foam area of the tread surface 10 to 500 through 4,000mum<2>, the coefficient of variation of each foaming area to 0.5 through 0.8, and foam occupation area to 10% through 35%.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applied to heavy-duty pneumatic tires with a normal air pressure of 5 kgf/1 or more, such as tires for large trucks, buses, light trucks, etc., specifically, general tires. The present invention relates to a heavy-duty pneumatic tire that has excellent frictional force (braking performance, driving performance) on icy and snowy roads without impairing running performance on roads (dry roads, wet roads).

[Conventional technology]

Conventionally, when driving a car in winter in a snowy and cold region, safety on snowy and icy roads is ensured by using spiked tires with spikes driven into the tires or by attaching tire chains to the outer circumference of the tires. There is. FIG. 3 shows an example of a tread pattern of a spiked tire. In FIG. 3, the tread surface 10 has three
The main groove 1 of the book is provided in an annular shape. Further, a plurality of lateral grooves 2 are provided in the tire width direction. A plurality of broncs 3 are defined by these main grooves 1 and lateral grooves 2. A plurality of spike bottles 5 are installed in the block 3.

However, tires equipped with spiked tires or tire chains are susceptible to road wear and damage, which becomes dust and causes pollution, posing a major environmental problem.

In order to solve such safety and environmental problems, standless tires that do not use spikes or chains and have braking performance on snowy and icy roads are rapidly becoming popular.

However, in conventional standless tires, the tread pattern formed on the tread surface is a kerfed block-like pattern, and snow tires (
Similar to snow road tires), the groove area ratio of the tread surface is 40.
% to about 50%, it exhibits maneuverability comparable to that of spiked tires on snowy roads, but its maneuverability on ice is insufficient. Therefore, if an attempt is made to lower the groove area ratio in order to improve the performance on ice, the performance on snow will decrease.

In order to improve the braking performance of such studless tires on icy roads, various proposals have been attempted in the past while keeping the groove area ratio at about 40% to 50%. For example, JP-A-55-135149, JP-A-58-19
As disclosed in Publication No. 9203 and Japanese Patent Application Laid-open No. 137945/1980, 1. By using a rubber composition containing a large amount of softener and plasticizer as resin rubber, the hardness at low temperatures can be lowered and it can be used on ice. Methods are known to improve performance.

However, if a large amount of softener or plasticizer is added to lower the hardness at low temperatures, performance on ice is improved, but problems tend to occur in terms of reduced braking performance and steering stability on wet road surfaces.

As an alternative to these studless tires, 1-
Some use foam rubber for the red part. Tires using such foamed rubber are disclosed, for example, in Japanese Patent Application Laid-Open No. 62-28300.
It is disclosed in Publication No. 1 and Japanese Patent Application Laid-Open No. 63-90402. However, in these tires, the hardness of the foamed rubber is low, so the engineering effect and drainage effect of the closed cells are not sufficient, and furthermore, the wear resistance and driving performance on ordinary roads (dry roads, wet roads) deteriorate. There is also a problem.

On the other hand, in order to improve these problems,
As described in Japanese Patent Application Laid-open No. 89547 and Japanese Patent Application Laid-Open No. 64-63401, short fibers are added to foamed rubber to increase the hardness of the torso part, and a part of the shoulder in the tread part is reinforced. Efforts are being made to improve driving performance, but it is still insufficient.

As described above, although a certain degree of improvement in ice and snow performance has been recognized, at present no standless tire has been obtained that simultaneously satisfies wear resistance and running performance on ordinary roads.

[Problems to be Solved by the Invention] The present invention provides a heavy-duty pneumatic tire with a normal air pressure of 5 kgf/1 or more, which significantly improves the frictional force on icy and snowy roads without impairing running performance on dry or wet roads (ordinary roads). The purpose is to provide

[Means to solve the problem]

The heavy-duty pneumatic tire of the present invention has a block pattern formed on the tread surface, a tread development width of 80% or more of the maximum width of the tire, and a groove area ratio of 30% to 45% on the tread surface. The foamed rubber is made of foamed rubber having closed cells, and the foamed rubber contains less than the same amount of urea-based auxiliary agent as the foaming agent, and the foamed rubber has a JIS hardness of 60 to 60 at 0°C. 74. The average bubble area on the tread surface is 500 to 4000 μm2, the coefficient of variation of each bubble area on the tread surface is 0.5 to 0.8, and the bubble occupation area ratio on the tread surface is 10% to 35%. shall be.

This means will be explained in detail below with reference to the drawings.

FIG. 1 is an explanatory half-sectional view in the meridian direction of the heavy-duty pneumatic tire of the present invention. In FIG. 1, the heavy-duty pneumatic tire A of the present invention has a normal air pressure of 5 kgf/cnl.
The above is the pair of left and right bead portions IL 11 and these bead portions 11. A pair of left and right sidewall portions 12 connected to 11. 12 and these sidewall portions 12.
It consists of a tread portion 13 arranged between 12 and 12. A carcass layer 14 is installed between the pair of left and right bead portions IL 11, and in the tread portion 13, heel 1 and sil5 are arranged so as to surround the outer periphery of the carcass layer 14. lO is the tread surface, and R is the maximum width of the tire.

111 In the present invention, as shown in FIG. 2, a plurality of main grooves l extending in the tire circumferential direction EEi are annularly provided on the tread surface 10. Further, a plurality of lateral grooves 2 are provided in the tire width direction. These main grooves l and lateral grooves 2
A plurality of blocks 3 are formed by. Blosoku 3
A plurality of sipes 4 are formed on the surface.

Sipe 7 of Sipe 4 formed on the surface of Brosoku 3
The width (distance between the sipes) is the width of the tresotho development (
It is preferably within the range of 5 to 20% of TI)W). In addition, the depth of the sipe 4 should be 50% or more of the depth of the main groove l, and in this case,
The depth of main a1 is preferably the same as the extra heavy tread of the groove depth in Explanation Table 9 on page 11 of JID D 4202 F Automotive Tire Specification Explanation.
It is recommended that the values be within the ranges listed in the columns for avy Tread (EIIT) and heavy tread (HT).

The spacing and depth of these sipes 4 are the same for all blocks 3.
Preferably, in accordance with the ground pressure distribution on the tread contact surface, the sipe pitch in areas with high ground pressure is large, and the sipe pitch in areas with low ground pressure is small.
It may be changed every 3 broncs. It is preferable that at least one end of the sipe 4 reaches the edge of the block 3 in order to provide tire performance on icy and snowy roads. Preferably, both ends of the sipe 4 reach the edge of the block 3, as shown in FIG. The direction of this sipe 4 is not particularly limited, and its shape can be a straight line, a curved line, a broken line, or the like.

Further, in the present invention, it is necessary that the tread development width (TDW) is 80% or more of the tire maximum width R. 80%
If it is less than that, there will be fewer land areas on the tread surface, the ground pressure per unit area will increase, and the edge effect and drainage effect brought about by closed cells will decrease. Furthermore, the stress on the block 3 provided with the lateral grooves 2 or the sipes 4 increases, and the block resistance also decreases.

Furthermore, in the present invention, the groove area ratio of the tread surface 10 is set to 3.
It is set at 0% to 45%.

Here, the groove area ratio is the ratio of the groove contact surface to the total area of the contact area (contact width x circumference) of the tread surface 10 under the conditions of maximum air pressure and maximum load specified in JATM^. It is calculated according to the following formula.

Total contact area of tread contact area + Groove area of tread contact area If this groove area ratio is less than 30%, the tire's performance on snow will decrease, and if it exceeds 45%, the land area on the tread surface 10 will decrease, resulting in This is because the Esoji effect and the edge effect of the closed-cell foamed rubber constituting the tread portion 13 are reduced, resulting in a reduction in performance on ice. For reference, conventional pneumatic tires for ice and snow roads have a groove area ratio of 40% to 50%. In the present invention, the 9 groove area ratio is reduced compared to the conventional one to improve performance on ice, and to compensate for the decrease in performance on snow, the tread portion 13 is made of foam having closed cells, as will be described later. By constructing it with rubber, the deterioration was suppressed.

The tire of the present invention that satisfies these requirements has the lateral grooves 2 and sipes 4 provided on the tread surface 10, which has a relatively large amount of land. m 2 and sipe 4, and by using closed-cell foam rubber in the tread portion l 3, the edge effect and drainage effect of the foam rubber are enhanced to effectively eliminate a thin water film on the icy and snowy road surface. As a result, ice and snow performance can be significantly improved.

(2) In the present invention, the tread portion 13 is made of foam rubber having closed cells. This foamed rubber contains a urea-based auxiliary agent in an amount less than the same amount as the foaming agent.

The inventors of the present invention have conducted extensive research to improve the frictional force on icy and snowy road surfaces, which has been difficult to achieve with conventional technology. It has been discovered that the above objectives can be achieved by using this method, leading to the present invention.

That is, it has been found that the closed cells contained in the foamed rubber improve the edge effect and drainage effect, and have a surprising effect especially on ice where a pseudo liquid layer exists at around 0°C. In addition, the conventional idea that low hardness at low temperatures improves ice and snow friction does not apply to foam rubber; rather, the fact that a certain degree of hardness significantly improves the edge effect and drainage effect brought about by closed cells in contact with the road surface. I found it. In addition, the relatively high hardness improves the rigidity of the tires, which has led to maintaining a high level of driving performance on general roads (dry roads and wet roads), which has been a weak point of conventional winter tires.

However, since the hardness of foamed rubber is significantly lower than that of non-foamed rubber, normally, in order to increase the hardness of foamed rubber, the hardness of matrix rubber is significantly increased to l 1 . Generally, adjustments are made such as increasing the amount of reinforcing agent such as carbon blank or greatly reducing the amount of softening agent such as oil, but this is not desirable as it deteriorates workability and heat generation. . Therefore, in order to lower the decomposition temperature of the blowing agent, the present inventors conducted various studies focusing on the fact that the urea-based auxiliary agent, which is often used in combination with the blowing agent, increases the crosslink density. As a result, even if a urea-based auxiliary agent is added alone to a rubber sole, the hardness increases, but
It was found that the effect is even greater when used in combination with a foaming agent. In other words, it was discovered that by adding a specific amount of urea-based auxiliary agent to the foaming agent, the decrease in hardness due to foaming could be suppressed and the hardness could be made to be comparable to that of non-foamed rubber, while also having negative effects on processability, heat generation, etc. It was also confirmed that there was no effect on Furthermore, if a nitroso compound is selected as the blowing agent, formaldehyde will be produced during the decomposition reaction and give a strong pungent odor, so in this case as well, a urea-based auxiliary agent that will accept aldehyde is added. Word production 1 2 It is very effective from a business perspective.

After obtaining this knowledge, the present inventors conducted repeated research on the distribution of air bubbles, tread patterns, etc., and arrived at the present invention.

In the present invention, the foamed rubber is made by adding a foaming agent to a conventional rubber compound, and further blending a urea-based auxiliary agent in an amount less than the same amount as the amount of the foaming agent.

Preferably, 30 to 90% by weight of the urea-based auxiliary agent is blended based on the amount of the blowing agent. If a urea-based auxiliary agent is not added, the hardness of foamed rubber will be significantly lower than that of non-foamed rubber, so it is necessary to significantly increase the amount of reinforcing agents such as carbon blank or significantly reduce the amount of softeners such as oil. Adjustment is required, which deteriorates processability and heat generation properties, and furthermore, when a blowing agent with a high decomposition temperature is used, it becomes difficult to manufacture tires at normal vulcanization temperatures. In addition, if a urea-based auxiliary agent is added in an amount equal to or more than the amount of the blowing agent, the effect of suppressing the decrease in hardness due to foaming becomes saturated, making it uneconomical, and depending on the blowing agent, the decomposition temperature may drop too much. In this case, the unvulcanized rubber may foam during the extrusion process.

In the present invention, in order to construct the tread portion of a heavy-duty pneumatic tire with foamed rubber having closed cells, a foaming agent and a urea-based auxiliary agent are usually added to the rubber composition used for the tread portion, and then Vulcanization may be performed according to the manufacturing method. In this case, the glass transition temperature of the foamed rubber may be such that the embrittlement temperature is -30° C. or lower so that cracks do not occur during winter use. As the blowing agent, any organic or inorganic blowing agent can be selected. For example, organic blowing agents include benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, azodicarbonate, etc., and inorganic blowing agents include sodium bicarbonate, ammonium carbonate, ammonium nitrite, and are not particularly limited. As the urea-based auxiliary agent, a compound of urea and an anti-aggregation agent, an acidic substance for preventing moisture absorption, etc., or urea alone is used. Specifically, for example, Eihe Kawei Industry's No. 1 cell base}
Examples include M3 (14 urea decacidic substance), Cellpaste M5 (urea decacidic substance), and Cellpaste}101 (urea decaggregation inhibitor). In addition, compounding agents such as carbon black, a softener, a processing aid, an anti-aging agent, a wax, a vulcanizing agent, and a vulcanization accelerator may be added in appropriate amounts according to the practice in the industry. However, it is preferable that the blowing agent be blended in an amount of 0.5 to 20 parts by weight based on 100 parts by weight of the raw rubber, especially in order to obtain the I-recycler of the present invention. Furthermore, as a method to improve performance on icy and snowy roads and on general roads, it is possible to further improve these performances by introducing a two-layer or three-layer toresoto structure such as the Kya Noputre Nodo Rubber/Heastread rubber structure. You will be able to do two things. Therefore, it is preferable.

In the present invention, the foamed rubber having closed cells constituting the toresoto part has the following requirements (1) to (2).

■ JIS hardness at 0°C is 60 to 74.

Here, JIS hardness refers to JIS-^ hardness.

The hardness of the foamed rubber is required to have a JTS hardness of l5 60 to 74 at 0°C, preferably 63 to 74.
It is 68. If the JIS hardness at 0°C is less than 60, the edge effect of bubbles and the drainage effect will decrease, and the braking performance on icy and snowy roads will deteriorate.
Drivability is not sufficient, and driving performance such as wear resistance and steering stability on general roads is also deteriorated, which is not preferable. If it exceeds 74, the performance on icy and snowy roads will deteriorate due to a decrease in adhesive friction force.

■ Average bubble area on the tread surface is 500 to 4000μ
Must be m2.

The average cell area of the foamed rubber needs to be closed cells of 500 to 4000 μm2, preferably 1000 μm2.
~3500 μm2. This is because if it is less than 500 μm2, the effect of improving performance on ice and snow roads will be insufficient, and if it exceeds 4000 μm2, wear resistance and running performance on ordinary roads will be significantly reduced.

■ The coefficient of variation of the area of each bubble on the tread surface is 0.5 to 0.
．． Must be 8.

As a result of investigating the shape and distribution of bubbles, it was found that the bubble distribution has a narrow distribution width, and that by optimizing the bubble shape and occupied area ratio, it is possible to simultaneously satisfy snow and ice 16 road performance and general road performance. by.

Here, the coefficient of variation (K) of closed cells is determined according to the following.

K = S/X . When this coefficient of variation (K) is less than 0.5, the performance on ice and snow roads and on ordinary roads deteriorates due to a decrease in the edge effect of bubbles, and when it exceeds 0.8, the performance on ice and snow decreases due to a decrease in the drainage effect of bubbles.

(2) The bubble occupation area ratio on the surface of Tresoto is 10% to 35%.

If it is less than 10%, the improvement effect on ice and snow road performance is small, and it is 35%.
This is because although the performance on icy and snowy roads is improved, the wear resistance and performance on ordinary roads are significantly reduced. The bubble occupation area ratio is expressed as the area ratio of the bubbles per unit area of the foamed rubber.

l7 Examples and comparative examples are shown below.

EXAMPLES AND COMPARATIVE EXAMPLES Various types of tires with the tire size shown in FIG. 2 and tire sizes of IIR 22.5 1 and IPR were manufactured.
These tires were evaluated as follows.

The results are shown in Table 1. In addition, 1. Red development width (T
D W) is 214mm, maximum tire width R is 266m+
i. The depth of the upper groove was 19.9 mm. The test vehicle used was a large vehicle (2/D). In addition, conventional tires have 60 spike pins driven into the tire block and do not use foam rubber.

Average bubble area, bubble dynamic coefficient, bubble occupancy area: A test piece was cut out from the tread of each test tire, made into a flat surface, and then imaged at 165x magnification using NEXUS 6400 manufactured by Kashiwagi Laboratory. The evaluation was based on the average value of the samples.

Sokka L dust: Cut out a test piece from the tread part of each test tire, and
Hardness was measured at a temperature of 0° C. in accordance with the method specified in IS-K6301.

Braking performance on icy roads: Braking from 40 km/h on icy roads was evaluated based on LJ and braking distance, and the results were expressed as an index with conventional tires set at 100. The larger this number is, the better the braking performance is.

Driving performance on a compacted snow road: When climbing a slope on a compacted snow road from an initial speed of 30kn+/h, depending on the required time, the tire was rated <T, and the conventional tires were compared with 10
Expressed as an index set to 0. The larger this value is, the better the drive performance is.

Steering stability (dry road surface): The feeling of each tire was scored by five test drivers using a 10-point system, and the results (average value) were expressed as an index relative to conventional tires. The larger the value, the better the steering stability.

{Abrasion resistance (dry road): After driving 20,000km on a dry road surface under the design normal load and air pressure conditions specified by JATMA, the amount of wear of each tire was expressed as an index of 19 compared to the amount of wear of conventional tires. .

The higher the value, the better the wear resistance. Show that you are good at it.

(Margins below the wooden page) 20 The following can be seen from Table 1.

(al Example 1, Comparative Example 1 Example 1 in which the urea-based auxiliary agent is blended as specified in the present invention
Well then... 115-A hardness and foaming state were both as specified, and the tire performance was also superior to conventional tires, whereas Comparative Example 1, which did not contain a urea-based auxiliary agent, had JI
The S-A hardness decreases significantly and falls outside the range specified in the present invention. In order to bring the hardness within the range defined by the present invention, for example, it is necessary to increase the amount of carbon blank or add i4{ffi oil, which is disadvantageous in terms of workability and heat generation.

(bl Examples 1 to 3, Comparative Example 2 In Examples 1 to 3, whose JIS-A hardness at 0°C is within the range specified by the present invention, not only the ice and snow performance is significantly improved compared to the conventional example. , its performance on public roads and its wear resistance are also very good.

On the other hand, in Comparative Example 2, in which the hardness was outside the specifications of the present invention, it was found that not only the improvement effect on ice and snow performance was small, but also the performance on ordinary roads and abrasion resistance were significantly lowered.

tel Examples 1 to 3, Comparative Example 3.4 Example 1 in which the average cell area and coefficient of variation are within the range specified in the present invention
-3, Comparative Example 3 where the average cell area is outside the specification of the present invention and Comparative Example 4 where the coefficient of variation is outside the specification of the present invention,
Although its performance and wear resistance on public roads are satisfactory, it has the disadvantage of poor ice and snow performance.

(d+ Examples 1 to 3, Comparative Example 5 Example 1 in which the bubble occupied area is within the range specified in the present invention
In contrast to Comparative Example 5, in which the bubble occupation area ratio is outside the specification of the present invention, although the ice and snow performance is improved, the performance on ordinary roads and the abrasion resistance deteriorate, which is not preferable.

(el Example 1, Comparative Example 6 Compared to Example 1, in which the groove area ratio was within the range specified by the present invention, Comparative Example 6, in which the groove area ratio was outside the range specified by the present invention, had inferior performance on snow. I understand that.

23 [Effects of the Invention] As explained above, according to the present invention, the normal air pressure is 5.
Closed-cell foamed rubber made by blending a specific proportion of a foaming agent and a urea-based auxiliary agent is used in the torrent part of a heavy-duty pneumatic tire of 0 kgf/ctK or more, and the average cell area and coefficient of variation of the foamed rubber are determined. , bubble occupation area ratio, and 0
By identifying the JIS 8 hardness at °C, and by forming a block pattern on the tread surface to determine the tread development width and groove area ratio,
Frictional force on icy and snowy road surfaces can be significantly improved without impairing driving performance.

[Brief explanation of the drawing]

FIG. 1 is an explanatory half-sectional view in the meridian direction of an example of a pneumatic tire for heavy loads according to the present invention, FIG. 2 is an explanatory plan view showing an example of a block pattern on the tread surface of this tire, and FIG.
The figure is an explanatory plan view showing an example of a tread pattern on the tread surface of a conventional spiked tire. 24 l...main groove, 2...horizontal groove, 3...brosock, 4...side, 5...spike pin, 10...tread surface.

Claims (1)

[Claims] A block pattern is formed on the tread surface, the tread development width is set to 80% or more of the tire maximum width, and the groove area ratio of the tread surface is set to 30% to 45%, and the tread portion is made of foamed rubber having closed cells. The foamed rubber contains less than the same amount of urea-based auxiliary agent as the foaming agent, and the foamed rubber has a JIS hardness of 6 at 0°C.
0 to 74, average bubble area on the tread surface is 500 to 40
00 μm^2, a coefficient of variation of the area of each bubble on the tread surface is 0.5 to 0.8, and a bubble occupation area ratio on the tread surface is 10% to 35%.